Nanoprinting with Crystal Engineering for Perovskite Lasers

Nanoprinting with Crystal Engineering for Perovskite Lasers | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Research Article Nanoprinting with Crystal Engineering for Perovskite Lasers Shiqi Hu, Ji Tae Kim This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-5651743/v1 This work is licensed under a CC BY 4.0 License Status: Posted Version 1 posted You are reading this latest preprint version Abstract Metal halide perovskites are promising laser light sources due to their exceptional optical gain and solution-processability. Structuring the cavity that determines lasing mode and performance, however, is mostly limited to chemical synthesis or in-plane multi-step lithographic processes, which lead to high shaping rigidity or poor lasing performance. Here, we introduce a direct electrohydrodynamic three-dimensional printing that produces freestanding, high-performance inorganic perovskite sub-micro lasers with tailored dimensions and locations, assisted by crystal engineering. The printed vertical nanowires exhibit excellent crystallinity after vapor-phase solvent engineering. Therefore, they show a high-performance two-photon pumped Fabry–Pérot mode vertical lasing with a threshold of 2.98 µJ/cm 2 , and our on-demand printing method provides the simplest route to tune the lasing characteristics such as lasing threshold and mode spacing, by adjusting the printed nanowire length. We demonstrated that the length-dependent lasing in the printed arrays can configure multi-level anticounterfeiting labels. We expect this additive manufacturing approach combined with crystal engineering to improve the design flexibility and performance of micro photonic circuitries. Mechanical Engineering 3D printing inorganic halide perovskites crystal engineering vertical geometry lasers anticounterfeiting Figures Figure 1 Figure 2 Figure 3 Figure 4 Introduction Over the past decade, inorganic lead halide perovskites, particularly CsPbX 3 (X = Cl, Br, I), have emerged as a promising semiconducting material for next-generation information technology 1 – 3 . They show great potential for diverse fields of applications including solar cells 4 – 6 , light-emitting diodes 7 , 8 , photodetectors 9 , 10 , and lasers 11 – 14 due to their outstanding optoelectronic properties 15 and solution processability 16 – 18 . Recently, extensive research has focused on excellent coherent light emission properties of perovskites for laser applications 14 , 19 – 21 . Many types of perovskite lasers in the forms of films, disks, and wires have successfully been devised for optical communication 22 , sensing 23 , and information storage 14 , 22 , 24 – 29 . Here, a key element to design and engineer lasing characteristics is tailoring the cavity geometry. To date, most of the perovskite research has been conducted in the form of a thin film 5 , 30 , 31 . Despite the solution processability, the fabrication of micro- and nanostructured perovskite lasers strongly relies on expensive lithographic techniques such as electron beam lithography 32 , 33 , photolithography 34 , 35 , imprinting 36 , 37 , and so on. Furthermore, multiple lithographic processes may be necessary for more sophisticated structuring 38 – 40 . Printing technology, e.g., inkjet printing, provides a simple and flexible route to fabricate large-area perovskite micropatterns with controlled geometries and locations 41 – 47 . However, the conventional approaches continue to suffer from the technological challenges associated with their poor spatial resolution and in-plane low aspect ratio, limiting the design and manufacture of miniaturized perovskite lasers. The utilization of chemically synthesized perovskite micro- and nanowires as a building block provides a beneficial route for miniaturization, however, their placement and assembly suffer from low-yield, labor-intensive processes. Moreover, most fabrication techniques render the nanowire a horizontal geometry in direct contact with the substrate along the entire length, leading to larger index matching and cavity loss 48 , 49 . In this work, we develop a nanoscale, crystal-engineered 3D printing method for fabricating vertical nanowires for high-performance lasing. We harness electrohydrodynamic (EHD) nanodripping to print CsPbBr 3 precursor nanodroplets directly on the substrate, followed by evaporation-driven crystallization. With the aid of electrostatic autofocusing, the EHD nanodripping produces a freestanding nanowire with tailored diameter, length, and placement. Subsequent vapor-phase solvent annealing significantly improves the crystallinity of the printed freestanding nanowire with large refractive index contrast with the surrounding air, leading to high-performance two-photon pumped lasing with a lasing threshold of 2.98 µJ/cm 2 . Benefiting from on-demand control of the nanowire length, we demonstrate the capability of selecting the lasing mode and modulating the mode spacing at will. This on-demand approach successfully demonstrates 3D printing of multi-level anticounterfeiting labels configured with sub-micrometer-sized pixels storing the information in individually programmed length-dependent-lasing threshold and mode spacing. The unique features of this method such as nanoscale resolution, lithography-free approach, and exceptional manufacturing flexibility will find a great advance in the practical realization of new-design photon sources. Results 3D printing process with two-step crystal engineering Figure 1 a depicts our EHD 3D printing process of vertical perovskite nanowires. A glass nanopipette (diameter: 450 nm, Figure S1) filled with CsBr + PbBr 2 precursor ink dissolved in dimethyl sulfoxide (DMSO) is placed above a glass substrate at a separation of 10 µm. A back electrode is located underneath the substrate. The positions of both the pipette and the substrate are controlled by three-axis stepping motors with sub-micrometer accuracy and millimeter displacement capability. When a high voltage of ~ 10 2 V is applied to the back electrode, an induced electrostatic stress acting on an ink meniscus exceeds the surface tension, and nano-sized ink droplets are ejected out of the pipette and land on the substrate. With the aid of mild substrate heating at 40°C and solvent evaporation, the concentration of the precursor rapidly reaches supersaturation, promoting the crystallization of CsPbBr 3 inside the deposited droplets, which refers to the first-step crystal engineering. Thanks to the electrostatic autofocusing effect 50 , the crystal grows vertically, forming a freestanding CsPbBr 3 nanowire with polycrystalline nature. Note that acquiring high crystallinity and accompanying smooth surface is crucial for lasing performance. To this end, a subsequent vapor-phase solvent annealing process (the second-step crystal engineering) is introduced to the as-printed nanowires. This annealing process uses methanol vapor with high polarity since it is absorbed on the surface of the as-printed structure to decrease the surface energy, leading to recrystallization (See Experimental Section) without shape deformation. Consequently, a high-quality laser cavity with lower surface roughness and excellent crystallinity can be obtained from the as-printed freestanding structure. Figure 1 b shows the real-time printing process when a pulsed voltage of 180 V with a frequency of 20 Hz and a duty cycle of 60% was applied to the substrate. The process produced a vertical CsPbBr 3 nanowire with a diameter of 550 nm and a length of 5 µm, within 5 seconds. The influences of substrate temperature, ink concentration, and applied voltage on the printing were examined. The thermodynamic driving force for crystallization can be quantified by the change in chemical potential $$\:\varDelta\:\mu\:=\:-RT\text{ln}\left(\frac{c}{{c}_{s}}\right)=-RT\text{ln}\sigma\:\:\:\:\left(1\right)$$ where \(\:c\) is the concentration of the precursor in the droplet, \(\:{c}_{s}\) is the solubility, \(\:R\) is the universal gas constant, \(\:T\) is the absolute temperature, and \(\:\sigma\:\) is the supersaturation ratio. First, we optimized the temperature for reliable printing. An increase in temperature causes the solvent to evaporate, promoting the supersaturation-driven crystallization. If the temperature is too high, it would accelerate the crystallization inside the nanopipette, leading to clogging. On the other hand, if the temperature is too low, solvent evaporation would be insufficient for driving crystallization, leading to the lateral spreading of the ejected ink droplet and end up with failure in vertical crystal growth. Second, the precursor concentration delivers a similar effect as the temperature does. Comprehensively, the diagram in Fig. 1 c shows the printability of a CsPbBr 3 nanowire at different temperatures and ink concentrations. We found a printing success region (marked in green circles) ranging the substrate temperatures from 30 to 50°C and the ink concentrations from 50 to 150 mM. Our EHD printing approach is general and therefore applicable to other perovskite compositions, as Figure S2 shows printed vertical CsPbI 3 and CsPbCl 3 nanowires. The diagrams of their printability are shown in Figures S3 and S4, respectively. The solvent for each perovskite precursor was selected by the consideration of the solubility and the boiling point. For example, a mixture of CH 3 NO + DMSO was used as a solvent for CsPbCl 3 precursor. The dependence of the vertical growth speed of perovskites on the applied voltage was quantitatively investigated. Figure 1 d plots a vertical growth speed of CsPbBr 3 as a function of an applied voltage. The printing was performed at a pipette-substrate distance of 10 µm, a substrate temperature of 40°C, and relative humidity (RH) of 10%. Three distinguishable regions were clearly observed. At a low voltage region below 150 V, no ink ejection was observed (blue cross marks). At a range of 150 V to 180 V, when the induced electrostatic stress acting on the ink meniscus exceeds the surface tension, a periodic ejection of ink nanodroplets produces a freestanding nanowire (green circles). In this region, the growth speed linearly increases with the voltage amplitude, as plotted by the inset of Fig. 1 d. At a voltage over 180 V, there is a big soar in the growth speed due to the ejection of a large-volume ink droplet with an electrostatically driven increase in the ink flow rate (red cross marks), which leads to lateral spreading. The growth speed–voltage dependencies of CsPbI 3 and CsPbCl 3 were also investigated, as shown in Figures S5 and S6, respectively. The applied voltage influences not only the vertical growth speed but also the diameter of the printed nanowire. Figure 1 e plots the dependence of the nanowire diameter on the applied voltage. The diameter increases with the voltage, resulting from the increases in the ink flow rate and subsquent limited lateral spreading. The voltage-diameter dependencies of CsPbI 3 and CsPbCl 3 were also demonstrated in Figure S7, exhibiting a similar trend as that of CsPbBr 3 . The results offer a simple, lithography-free route to control the dimension of an individual freestanding nanowire. To verify the reliability of the printing, we printed a 20 × 20 array of vertical CsPbBr 3 nanowires with programmed heights (Figs. 1 f and 1 g). We also fabricated an ‘HKU’-shaped nanopattern consisting of three compositions with different emission wavelengths, H: CsPbI 3 ; K: CsPbBr 3 ; U: CsPbCl 3 (Figure S8). Furthermore, the universality of our method was demonstrated by the fabrication of CH 3 NH 3 PbX 3 (X = Cl, Br, I) nanowires, as shown in Figure S9. The printed nanowires were thermally annealed under 70℃ before the characterization. The as-printed CsPbBr 3 nanowire exhibited a polycrystalline nature, as confirmed by the field emission scanning electron microscope (FE-SEM) image, the selected area electron diffraction (SAED) analysis and the bright-field transmission electron microscope (TEM) image in Fig. 1 h, 1 i, and 1 j, respectively. We remark the vapor-phase solvent annealing improves the crystallinity and the surface smoothness without any structural collapse. The FE-SEM image of Fig. 1 k shows a smooth surface of the printed nanowire after the solvent annealing. Furthermore, the solvent annealing process made a great advancement in improving the crystallinity, as shown in Fig. 1 l. The SAED pattern exhibits a single crystal-like pattern which confirmed that the increased grain size and the corresponding HR-TEM image (Fig. 1 m ) also verified the highly ordered crystallinities of the CsPbBr 3 crystals which enable them to act as a high-quality laser cavity. The bright-field TEM image in Figure S10 also demonstrates the improvement on surface smoothness. Lasing of 3D printed perovskite nanowires The printed vertical CsPbBr 3 nanowire treated with solvent annealing performs high-performance room-temperature lasing, as it acts as a gain medium and high-quality cavity simultaneously. The resulting nanowire geometry provides the designed cavity length and the reflective end facets. It is worth noting that our EHD printing can produce freestanding vertical CsPbBr 3 nanowires, rendering a vertical geometry that leads to large refractive index mismatch and lower cavity loss. The refractive index contrast between the vertical CsPbBr 3 nanowire (n = 2.3) and the environment (air, n air = 1.0 for one end, glass, n glass = 1.5 for the other end) develops more efficient facet reflection and waveguiding along the nanowire than the conventional in-plane geometry. The lasing was stimulated by a two-photon pumped excitation using an 800 nm femtosecond laser at room temperature. The kinetics of two-photon absorption (2PA) is summarized in Figure S11. Figure 2 a shows the photoluminescence (PL) spectra of a vertical CsPbBr 3 nanowire with a length of 50 µm, excited with different pump fluences. At a pump fluence, P = 1.58 µJ cm − 2 , the spontaneous emission with relatively broad spectra width was dominated (blue spectrum). With increasing the pump fluence (P ≥ 2.98 µJ cm − 2 ), the emission spectra contain a set of sharp peaks at λ ≈ 542 nm, exhibiting the stimulated emission. It is clearly shown that the FP-mode lasing of the nanowire was produced at high pump fluences. Figure 2 b plots the emission intensity (left axis, light input-light output, or ‘L-L’ curve, red) and the full width at half maximum (FWHM) of the primary peak at λ ≈ 542 nm (right axis, blue) as a function of the pump fluence, showing clear evidence of the lasing action. We observed a transition from spontaneous emission to stimulated emission at a threshold of 3.12 µJ cm − 2 . At above the threshold, the lasing peak intensity increases linearly with the pump fluence. The FWHM of the peak at λ ≈ 542 nm was drastically narrowed down from 12 nm to 0.2 nm at the threshold pump fluence, confirming the occurrence of lasing. The quality factor of this nanowire laser, defined as Q = λ/FWHM, was measured as ≈ 2700. The inset in Fig. 2 b plots the emission intensity as a function of the detection polarization angle, confirming a linearly polarized lasing emission. The vapor-phase solvent annealing significantly influences the lasing threshold. As the solvent annealing time increased from 0 (thermal annealed) to 3 hours, the lasing threshold decreased from 60.48 µJ cm − 2 to 3.12 µJ cm − 2 as plotted in Fig. 2 c. Similarly, the pump fluence value at the sharp FWHM drop decreased as the solvent annealing time increased (Fig. 2 d). The dependence of the lasing threshold on the solvent annealing time is plotted in Fig. 2 e. The lasing threshold successfully descended down to 2.98 µJ cm − 2 as the annealing lasted 20 hours. A plateau region was observed due to the limited interdiffusion length of the solvent vapor which accounts for the saturation of the solvent annealing effects 51 . The effect of the vertical configuration on the lasing performance was investigated and summarized in Fig. 2 f. The lowest lasing threshold of 6.848 µJ cm − 2 was obtained from a vertical nanowire with solvent annealing, whereas the highest threshold of 43.636 µJ cm − 2 was obtained from the as-printed nanowire lying on the substrate. Notably, our freestanding CsPbBr 3 nanowires exhibited a better lasing performance regarding the lasing threshold and Q factor than those lying on the in-plane substrate obtained from other conventional methods ( Fig. 2 g ) . Bespoke nanowire lasers Our 3D printing approach provides exceptional flexibility to tailor the nanowire dimension, that is the geometry of the laser cavity. In this study, we demonstrated on-demand length control of the nanowire for individual modulation of lasing characteristics, as depicted in Fig. 3 a. The nanowire length is a key parameter to tuning the lasing action in FP mode. Figure 3 b shows lasing spectra for freestanding nanowires with a diameter of 850 nm and different lengths, L from 10 µm, 14 µm, 20 µm, 30 µm, 40 µm, to 50 µm, under femtosecond pulsed laser excitation (800 nm, 50 fs, 1 kHz). In the spectra, the number of modes showed a descending trend when decreasing L and as a result, a single-mode lasing spectrum was acquired at L = 10 µm. All the spectra present a series of peaks with different mode spacing (△λ) values. It is noteworthy that the mode spacing, △λ is found to have a linear relationship with the reciprocal of L . According to the FP mode laser theory, the equation △λ = λ 2 /2n g L (n g : group refractive index of the gain material, L : length of the nanowire, λ: emission wavelength) agrees with the experimental results (Fig. 3 c). From the linear fitting of △λ – 1/ L relation with a slope of 68, n g of the printed CsPbBr 3 nanowire at λ ≈ 542 nm is determined to be 2.2, which is consistent with the reported value of 2.3 52 . The lasing threshold decreases as L increases, as plotted in Fig. 3 d. This trend may be attributed to the gain volume change as the length, similar to that seen in the previous report 53 . Freestanding nanowire lasers as cryptographic primitives. The ability of our technique to tailor nanowire lasers leads to high-resolution printing of multilevel anticounterfeiting labels. For a proof-of-concept demonstration, we fabricated a 4 × 4 matrix code consisting of vertical CsPbBr 3 nanowires with two different lengths of 30 µm and 15 µm for pixels, as depicted in Fig. 4 a. The nanowires have a diameter of 850 nm with a pitch (wire-to-wire distance) of 15 µm. The first level of security comes from the nanowires’ small diameter with a vertical configuration, only visible via a high-magnification microscope (Fig. 4 b). A second security level is that the fluorescence nature of the perovskite nanowires is only accessible by specific light excitation with an appropriate wavelength, as demonstrated in Fig. 4 c. We point out that the nanowire’s length-dependent-lasing can be another level of cryptographic primitive. At a relatively low pump fluence of 10 µJ/cm 2 , all 16 pixels in the printed matrix code exhibited broad spontaneous emissions corresponding to the fluorescence of CsPbBr 3 (Fig. 4 d). Their indistinguishable emission spectra may protect the nanowire length information from duplication. At a pump fluence of 30 µJ/cm 2 , the pixels configured with the 30 µm-length nanowire exhibited lasing action due to their lower lasing threshold value (22.8 µJ/cm 2 ) than the applied power, whereas the others still exhibited spontaneous emission, as shown in Fig. 4 e. The result demonstrates that the pump fluence can be a cipher key for accessing the length-dependent laser characteristics of the nanowire pixels. When the pump fluence exceeds 50 µJ/cm 2 , all 16 pixels exhibited lasing emissions but their different mode spacings (△λ) depended on the nanowire lengths (Fig. 4 f). The average △λ values for the 30 µm and 15 µm-length nanowires were 2.18 ± 0.15 nm and 4.02 ± 0.21 nm, respectively. Figure 4 g shows the mode spacing mapping of the corresponding matrix code at 50 µJ/cm 2 . This length-dependent △λ can be used as a cryptographic primitive and Figs. 4 h and i show examples of how to decrypt △λ information of individual pixels. Figure 4 h shows a △λ-based quick-response (QR) code generated by a condition if “1” denotes “△λ > 3 nm” and “0” denotes else. The △λ-based QR code can be variable. The reversed QR code is generated by changing the condition to if “1” denotes “△λ < 3 nm” and “0” denotes else (Fig. 4 i). It is noteworthy that such encoded mode spacing can only be decrypted by high-precision analysis of the lasing spectra, inaccessible via conventional imaging. From this, we show that we can freely encrypt information in the length of the vertical nanowire pixel and read it out by analyzing the lasing mode spacing, which offers another level of security for these anticounterfeiting labels. Last but not least, the data-storage capacity and security level can be easily enhanced by a combination of different nanowire lengths and compositions via our advanced 3D printing technique. Discussion In this work, we have developed a nanoscale electrohydrodynamic 3D printing method combined with vapor-phase solvent engineering to directly print freestanding perovskite nanowire lasers. This method enables on-demand, precise control over dimension and placement in miniaturized perovskite lasers, by which the two photon-pumped emission characteristics can be tailored at will. Furthermore, subsequent vapor-phase solvent annealing improves the crystallinity of printed nanowires which makes a joint contribution with the vertical geometry to the high-performance lasing. CsPbBr 3 vertical nanowires with different lengths were successfully fabricated, which were found to realize FP mode lasing with programmed mode spacing and threshold power. The proof-of-concept experiments demonstrate multi-level cryptographic anticounterfeiting labels configured with 3D perovskite nanopixels with individually programmed lasing characteristics, which are inaccessible via conventional optical imaging apparatus. These results provide the engineering basis for the function-oriented design of diverse perovskite laser devices without the restriction of traditional lithographic processes and the novel insight into high-resolution information encryption and storage. Materials and Methods 7.1 Materials and Synthesis of Functional Inks : Cesium iodide (CsI, 99.998%, purchased from Alfa Aesar) and lead (II) iodide (PbI 2 , 99%, purchased from Sigma Aldrich), Cesium bromide (CsBr, 99.999%, purchased from Alfa Aesar) and lead (II) bromide (PbBr 2 , 99%, purchased from TCL), Cesium chloride (CsCl, 99.999%, purchased from Alfa Aesar) and lead (II) chloride (PbCl 2 , 99%, purchased from TCL) were used as solutes. Dimethyl sulfoxide (DMSO) (99.7%, purchased from Acros), and formamide (CH 3 NO, 99.5%, purchased from Acros) were used as solvents. 0.3 M CsPbI 3 precursor solution ink was prepared by dissolving 0.3 mmol CsI and 0.3 mmol PbI 2 into 1 mL DMSO with overnight stirring at 70 °C for a concentration of 0.3 M. 0.075 M CsPbBr 3 precursor solution ink was prepared with dissolving 0.075 mmol CsBr and 0.075 mmol PbBr 2 into 1 mL DMSO with overnight stirring at 70 °C. 0.1M CsPbCl 3 precursor solution ink was prepared by dissolving 0.1 mmol CsCl and 0.1 mmol PbCl 2 into 1 mL CH 3 NO with overnight stirring at 70 °C and then diluted by DMSO with a volume ratio of 2:1. The ink preparation was performed in a glovebox with controlled oxygen concentration and humidity. 7.2 Preparation of Nozzles : 450 nm-aperture borosilicate nanopipettes (filament embedded, purchased from World Precision Instruments) were fabricated by a programmed heat-pulling process (P-97 Flaming/Brown Micropipette Puller, purchased from Sutter Instrument). Only pipettes with good nozzle quality, that is to say, with no cracks, or chipped edges were used. The pipette diameter was characterized using an FE-SEM (LEO 1530, Zeiss) installed at the Electron Microscope Unit of the University of Hong Kong. 7.3 Preparation of Substrates : The glass substrate were cleaned by 5-min ultrasonication in successive volumes of acetone, isopropyl alcohol, ethanol, and deionized water. 7.4 3D Printing Process : The printing machine consists of an ink-filled nanopipette and a glass substrate, which is spatially controlled by using a three-axis (x, y, z) stepping motor stage (XA05A, ZA05A, Kohzu Precision). Their positions and moving speeds are accurately controlled in real-time under custom-made software. The ink was introduced to the backside opening of the pipette and drawn to the very tip by capillary forces without applying any pressure. Given the small nozzle size, minimal caution was necessary when handling them. The pipette-substate distance was assured by a z-axis movement of the motor stage. The printing process was accomplished by applying a voltage to the glass substrate. The applied voltage was generated by a waveform generator and a high-voltage amplifier. During the printing process, the glass substrate was heated up to 40 °C to accelerate the perovskite crystallization and avoid lateral spreading. After printing, the glass substrate with perovskite nanowires was annealed at 70 °C for 10 mins to make it fully crystallized. The printing process was monitored in real-time by using a side-view optical microscope consisting of a 50× long working distance objective (Mitutoyo) and a camera equipped with a complementary metal-oxide-semiconductor sensor (DCC1545M, Thorlabs). The entire printing process was performed inside a custom-made environmental enclosure (filled with nitrogen gas) at controlled relative humidity and temperature. 7.5 Sample Characterizations : Full characterizations of 3D printed structures were performed in various aspects. The exteriors of the printed nanostructures were characterized by FE-SEM (Zeiss Leo 1530). The chemical compositions were quantitatively analyzed by energy-dispersive X-ray spectroscopy under a 20-kV electron beam of the Leo 1530. The characterization of the 3D printed structures’ crystallinity at a single entity level was conducted with a transmission electron microscope (TEM, FEI Tecnai G2 operating at 300 kV). For preparing the TEM samples, the 3D printed structures were directly fabricated onto a TEM grid (Ted Pella, lacey carbon type-A support film, 300 mesh, copper). Before these characterizations, all the fabricated samples were annealed at 70 °C for 10 mins. 7.6 Vapor-Phase Solvent Engineering Process : the as-printed structure on a glass substrate was put in a petri-dish with a radius 9 cm of and a depth of 1.5 cm. And 20 ml of methanol was injected into the petri-dish. The solvent annealing process was happening in the glove box at room temperature. 7.7 Laser Measurements : For the laser measurements, a schematic of the laser characterization setup is illustrated in Figure S15. Samples with CsPbBr 3 freestanding nanowires with different lengths were fabricated on a glass substrate by the same protocol mentioned above. The samples were located inside a chamber (Linkam DSC 600 temperature controller stage) connected to a rotary pump. A Ti: sapphire femtosecond laser (Coherent Libra) integrated with an optical parametric amplifier (Coherent OPerA Solo), which generates femtosecond pulses (50 fs, 1 kHz) at 800 nm, was used as the excitation source. The microscope (Olympus BX-52) and an objectives lens (20*0.8 NA objectives lens) were used to focus the femtosecond laser beam to a 200 µm diameter spot. The freestanding nanowires on the substrates were excited by the laser spot. The light emitted from the samples was collected by a conventional charge-coupled device (CCD) camera for the recording of the near-field image or attached to a monochromator (Princeton SpectraPro 2750 integrated with a ProEM EMCCD camera with a spectral resolution less than 0.1 nm) for spectrum analysis. Declarations A cknowledgements This work was supported by the General Research Fund (17208218, 17208919, 17204020) from the Research Grants Council of Hong Kong; the National Natural Science Foundation of China/Research Grants Council Joint Research Scheme (N_HKU743/22); Seed Fund for Basic Research (201910159047, 202111159097) from University Research Committee (URC), The University of Hong Kong; PolyU (RGC) nos. G-UALA, BBA5, ZVDJ and YBVJ; and Sichuan Natural Science Foundation (2022YFH0108); the National Research Foundation of Korea (NRF) grant funded by the Korea government (MSIT) (No. RS-2024-00407084). J.R. acknowledges the National Research Foundation (NRF) grant (RS-2024-00356928) funded by the Ministry of Science and ICT (MSIT) of the Korean government. Contributions Shiqi Hu designed and performed the experiments and analyzed the data. Ting Wang, Siu Fung Yu contributed to the laser optical characterization and analyzed the data. Mojun Chen, Yu Liu, Heekwon Lee, Jihyuk Yang, Xiao Huan, Tianyu Jiang, Cherry Park, Nara Jeon contributed to the optimization of the 3D printing process and gave helpful discussion. Zhiwen Zhou and Shien-Ping Feng contributed to the ink preparation. Shiqi Hu and Ji Tae Kim wrote the original manuscripts, and Ting Wang, Siu Fung Yu, Junsuk Rho, Mingjian Yuan also contributed to revising the manuscripts. Ji Tae Kim and Junsuk Rho supervised the project. All authors contributed to the data analysis and have approved the final version of this manuscript. Shiqi Hu, Ting Wang, Zhiwen Zhou contributed to this work equally. 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Photolithographic Patterning of Perovskite Thin Films for Multicolor Display Applications. Nano Letters 20 , 3710-3717 (2020). Liu W, Wang J, Xu X, Zhao C, Xu X, Weiss PS. Single-Step Dual-Layer Photolithography for Tunable and Scalable Nanopatterning. ACS Nano 15 , 12180-12188 (2021). Harwell J, Burch J, Fikouras A, Gather MC, Di Falco A, Samuel IDW. Patterning Multicolor Hybrid Perovskite Films via Top-Down Lithography. ACS Nano 13 , 3823-3829 (2019). Zhizhchenko A , et al. Single-Mode Lasing from Imprinted Halide-Perovskite Microdisks. ACS Nano 13 , 4140-4147 (2019). Wang Y , et al. Colorful Efficient Moiré-Perovskite Solar Cells. Advanced Materials 33 , 2008091 (2021). Sun K , et al. Three-dimensional direct lithography of stable perovskite nanocrystals in glass. Science 375 , 307-310 (2022). Zhang N , et al. Highly Reproducible Organometallic Halide Perovskite Microdevices based on Top-Down Lithography. Advanced Materials 29 , 1606205 (2017). Xing D , et al. Self-Healing Lithographic Patterning of Perovskite Nanocrystals for Large-Area Single-Mode Laser Array. Advanced Functional Materials 31 , 2006283 (2021). Chen M , et al. 3D Nanoprinting of Perovskites. Advanced Materials 31 , 1904073 (2019). Wang K, Xing G, Song Q, Xiao S. Micro- and Nanostructured Lead Halide Perovskites: From Materials to Integrations and Devices. Advanced Materials 33 , 2000306 (2021). Gu Z , et al. Direct-Writing Multifunctional Perovskite Single Crystal Arrays by Inkjet Printing. Small 13 , 1603217 (2017). Chen M , et al. Three-Dimensional Perovskite Nanopixels for Ultrahigh-Resolution Color Displays and Multilevel Anticounterfeiting. Nano Letters 21 , 5186-5194 (2021). Hu S , et al. Three-Dimensionally Printed, Vertical Full-Color Display Pixels for Multiplexed Anticounterfeiting. Nano Letters 23 , 9953-9962 (2023). Chen M , et al. 3D Printing of Arbitrary Perovskite Nanowire Heterostructures. Advanced Functional Materials 33 , 2212146 (2023). Hu S, Huan X, Liu Y, Cao S, Wang Z, Kim JT. Recent advances in meniscus-on-demand three-dimensional micro- and nano-printing for electronics and photonics. International Journal of Extreme Manufacturing 5 , 032009 (2023). Maslov AV, Ning CZ. Reflection of guided modes in a semiconductor nanowire laser. Applied Physics Letters 83 , 1237-1239 (2003). Gargas DJ, Toimil-Molares ME, Yang P. Imaging Single ZnO Vertical Nanowire Laser Cavities Using UV-laser Scanning Confocal Microscopy. Journal of the American Chemical Society 131 , 2125-2127 (2009). Galliker P, Schneider J, Eghlidi H, Kress S, Sandoghdar V, Poulikakos D. Direct printing of nanostructures by electrostatic autofocussing of ink nanodroplets. Nature Communications 3 , 890 (2012). Xiao Z, Dong Q, Bi C, Shao Y, Yuan Y, Huang J. Solvent Annealing of Perovskite-Induced Crystal Growth for Photovoltaic-Device Efficiency Enhancement. Advanced Materials 26 , 6503-6509 (2014). Yan D, Shi T, Zang Z, Zhao S, Du J, Leng Y. Stable and low-threshold whispering-gallery-mode lasing from modified CsPbBr3 perovskite quantum dots@SiO2 sphere. Chemical Engineering Journal 401 , 126066 (2020). Saxena D , et al. Optically pumped room-temperature GaAs nanowire lasers. Nature Photonics 7 , 963-968 (2013). Du W , et al. Strong Exciton–Photon Coupling and Lasing Behavior in All-Inorganic CsPbBr3 Micro/Nanowire Fabry-Pérot Cavity. ACS Photonics 5 , 2051-2059 (2018). Wu Z , et al. All-Inorganic CsPbBr3 Nanowire Based Plasmonic Lasers. Advanced Optical Materials 6 , 1800674 (2018). Wang X , et al. High-Quality In-Plane Aligned CsPbX3 Perovskite Nanowire Lasers with Composition-Dependent Strong Exciton–Photon Coupling. ACS Nano 12 , 6170-6178 (2018). Fu Y , et al. Broad Wavelength Tunable Robust Lasing from Single-Crystal Nanowires of Cesium Lead Halide Perovskites (CsPbX3, X = Cl, Br, I). ACS Nano 10 , 7963-7972 (2016). Wang Y , et al. Temperature Difference Triggering Controlled Growth of All-Inorganic Perovskite Nanowire Arrays in Air. Small 14 , 1803010 (2018). Liu Z , et al. Temperature-dependent photoluminescence and lasing properties of CsPbBr3 nanowires. Applied Physics Letters 114 , 101902 (2019). Tian J , et al. Gain-switching in CsPbBr3 microwire lasers. Communications Physics 5 , 160 (2022). Additional Declarations The authors declare no competing interests. Cite Share Download PDF Status: Posted Version 1 posted You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. As a division of Research Square Company, we’re committed to making research communication faster, fairer, and more useful. We do this by developing innovative software and high quality services for the global research community. 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Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-5651743","acceptedTermsAndConditions":true,"allowDirectSubmit":true,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":390716925,"identity":"d35fdd99-92d5-4cea-a975-47604a026002","order_by":0,"name":"Shiqi Hu","email":"","orcid":"","institution":"POSTECH","correspondingAuthor":false,"prefix":"","firstName":"Shiqi","middleName":"","lastName":"Hu","suffix":""},{"id":390717001,"identity":"d04e8efe-1e83-4ca0-91be-392c01c51313","order_by":1,"name":"Ji Tae Kim","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAA5klEQVRIie2PsQrCMBCGTwJ1CbhGlPYJhJRC0clXaRDi4gN0LBTaRXDVt7EU2qUP0OIiCM4dC2YwUcEtcXTIt1y448v9B2Cx/CGj9FUiDONMlncTGRT0UXClFGpWPnP5PeHq8YOC8knR98Dni9Od9VchYJKfURDrg6HpEXY4vPCSsIwCaSLEGsMtMwyxVLYJYYkM1gIqEsOWh1BKV6dDJCh4PyjODFSw1qlI5FCgUmEGJVztKcdhw/mSZQH2G5b6OsU/FLd2iDfrsK6CbhCu69ZlOdUqryH9NrDcrBMAPO3UYrFYLIonptBFUhbJnEAAAAAASUVORK5CYII=","orcid":"","institution":"KAIST","correspondingAuthor":true,"prefix":"","firstName":"Ji","middleName":"Tae","lastName":"Kim","suffix":""}],"badges":[],"createdAt":"2024-12-16 08:09:04","currentVersionCode":1,"declarations":{"humanSubjects":false,"vertebrateSubjects":true,"conflictsOfInterestStatement":false,"humanSubjectEthicalGuidelines":false,"humanSubjectConsent":false,"humanSubjectClinicalTrial":false,"humanSubjectCaseReport":false,"vertebrateSubjectEthicalGuidelines":true},"doi":"10.21203/rs.3.rs-5651743/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-5651743/v1","draftVersion":[],"editorialEvents":[],"editorialNote":"","failedWorkflow":false,"files":[{"id":71631989,"identity":"5226b923-b5bb-4e21-9589-543bb1c6a496","added_by":"auto","created_at":"2024-12-17 09:41:17","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":2648799,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eElectrohydrodynamic (EHD) 3D nanoprinting of perovskites with two-step crystal engineering\u003c/strong\u003e. \u003cstrong\u003ea,\u003c/strong\u003e Schematic illustration of EHD printing of a freestanding CsPbBr\u003csub\u003e3\u003c/sub\u003e nanowire with two-step crystal engineering, i. Supersaturation-driven crystallization, ii. Vapor phase solvent annealing. \u003cstrong\u003eb,\u003c/strong\u003e A series of side-view optical micrographs showing EHD printing of a freestanding CsPbBr\u003csub\u003e3\u003c/sub\u003e nanowire. The diameter of a glass nanopipette filled with CsBr + PbBr\u003csub\u003e2\u003c/sub\u003e solution dissolved in DMSO is 800 nm (scale bar: 2 µm). A pulsed voltage of 180 V (frequency: 20 Hz, duty cycle: 60%) is applied to the glass substrate for the ejection of nano-ink droplets. The printing process is completed within 5 sec. (scale bar: 2 µm) \u003cstrong\u003ec,\u003c/strong\u003e Phase diagram showing the printability of a CsPbBr\u003csub\u003e3\u003c/sub\u003e nanowire at different ink concentrations and temperatures (blue empty square: lateral spreading of ejected droplets, green solid circle: vertical printing, red empty pentagon: clogging of a nanopipette). \u003cstrong\u003ed,\u003c/strong\u003e Dependence of vertical growth speed on applied voltage at a fixed pipette-substrate distance of 10 µm (blue cross mark: no jetting, green circle: vertical growth, red cross mark: lateral spreading of excessively ejected droplets). \u003cstrong\u003ee,\u003c/strong\u003e Dependence of grown diameter on applied voltage at a fixed pipette-substrate distance of 10 µm. \u003cstrong\u003ef,\u003c/strong\u003e Side view FE-SEM image of a 20 × 20 array of freestanding as-printed CsPbBr\u003csub\u003e3\u003c/sub\u003e nanowires with controlled heights and a pitch of 10 µm (scale bar: 10 µm). \u003cstrong\u003eg,\u003c/strong\u003e the magnified image (scale bar: 5 µm). \u003cstrong\u003eh,\u003c/strong\u003e FE-SEM image of the as-printed freestanding nanowires with thermal annealing treatment (scale bars: 1 µm). \u003cstrong\u003ei, \u003c/strong\u003ecorresponding SAED patterns and \u003cstrong\u003ej, \u003c/strong\u003eHR-TEM images showing the polycrystallinity of the as-printed structure (scale bar: 2 1/nm). \u003cstrong\u003ek,\u003c/strong\u003e FE-SEM images of the printed freestanding nanowires after 3-hour solvent annealing showing improved surface roughness and uniform chemical composition (scale bars: 1 µm). \u003cstrong\u003el,\u003c/strong\u003e corresponding SAED patterns and \u003cstrong\u003em, \u003c/strong\u003eHR-TEM images show the improved crystallinity of the printed structure thanks to solvent annealing (scale bar: 2 1/nm).\u003c/p\u003e","description":"","filename":"1.png","url":"https://assets-eu.researchsquare.com/files/rs-5651743/v1/8694127ed4c9dcea0e67a38b.png"},{"id":71631986,"identity":"bc9ad964-95d6-487c-b32c-d622ad2e3f58","added_by":"auto","created_at":"2024-12-17 09:41:17","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":1040508,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eSolvent annealing effects on the 3D printed CsPbBr\u003c/strong\u003e\u003csub\u003e\u003cstrong\u003e3\u003c/strong\u003e\u003c/sub\u003e\u003cstrong\u003e lasing\u003c/strong\u003e. \u003cstrong\u003ea, \u003c/strong\u003eEmission spectra of\u003cstrong\u003e \u003c/strong\u003ea freestanding CsPbBr\u003csub\u003e3\u003c/sub\u003e nanowire with a height of 50 µm at different pump fluences. Femtosecond laser (50 fs, 1kHz) with a wavelength of 800 nm was used for two-photon excitation. The insets are the top-view optical PL images of the nanowire above (bottom) and below the threshold (top). \u003cstrong\u003eb,\u003c/strong\u003e Emission intensity and full width at half maximum (FWHM) at 542 nm as a function of pump fluence. (Inset) Polarization-dependent laser emission intensity. \u003cstrong\u003ec,\u003c/strong\u003e Dependence of emission intensity on pump fluence with different solvent annealing time. \u003cstrong\u003ed,\u003c/strong\u003e FWHM as a function of pump fluence with different solvent annealing time. \u003cstrong\u003ee,\u003c/strong\u003e Lasing threshold of a freestanding nanowire with a height of 50 µm as a function of solvent annealing time. \u003cstrong\u003ef, \u003c/strong\u003eLasing threshold comparison for different cavity geometry w/ or w/o solvent annealing.\u003cstrong\u003e g,\u003c/strong\u003e the lasing performance in terms of lasing threshold and Q factor are compared with other CsPbBr\u003csub\u003e3\u003c/sub\u003e nanowire-based lasing with a horizontal geometry fabricated with other techniques. Our work shows a lasing threshold of 2.98 µJ/cm\u003csup\u003e2\u003c/sup\u003e and a Q factor of 2700\u003csup\u003e13, 54-60\u003c/sup\u003e.\u003c/p\u003e","description":"","filename":"2.png","url":"https://assets-eu.researchsquare.com/files/rs-5651743/v1/ac805a04c432aafb04a2487c.png"},{"id":71633014,"identity":"797f3b04-1f45-4dbc-ad34-f6e1dca2023a","added_by":"auto","created_at":"2024-12-17 09:49:17","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":1312700,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eProgrammable freestanding nanowire lasers\u003c/strong\u003e. \u003cstrong\u003ea, \u003c/strong\u003eOn-demand EHD printing of\u003cstrong\u003e \u003c/strong\u003eCsPbBr\u003csub\u003e3\u003c/sub\u003e nanowires with controlled height for modulating lasing their lasing action. \u003cstrong\u003eb,\u003c/strong\u003e Emission spectra of\u003cstrong\u003e \u003c/strong\u003ethe printed CsPbBr\u003csub\u003e3\u003c/sub\u003e nanowires with \u003cem\u003eL\u003c/em\u003e = 10, 14, 20, 30, 40, and 50 µm under femtosecond laser excitation (800 nm, 50 fs, 1kHz), and corresponding optical micrographs showing printed freestanding CsPbBr\u003csub\u003e3 \u003c/sub\u003enanowires with different heights (L) from10, 14, 20, 30, 40, to 50 µm.\u0026nbsp; \u003cstrong\u003ec,\u003c/strong\u003e Mode spacing versus 1/\u003cem\u003eL\u003c/em\u003e, confirming the Fabry-Pérot mode lasing. \u003cstrong\u003ed,\u003c/strong\u003e Lasing threshold versus \u003cem\u003eL\u003c/em\u003e.\u003c/p\u003e","description":"","filename":"3.png","url":"https://assets-eu.researchsquare.com/files/rs-5651743/v1/ab9e7e9dc77346765190d05f.png"},{"id":71633012,"identity":"8741933e-2d9f-4044-b05c-869b90c16d5a","added_by":"auto","created_at":"2024-12-17 09:49:17","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":1207060,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003e3D printed lasing nanopixels as cryptographic primitives\u003c/strong\u003e. \u003cstrong\u003ea, \u003c/strong\u003eSchematic design, \u003cstrong\u003eb,\u003c/strong\u003e bright-field optical image and \u003cstrong\u003ec,\u003c/strong\u003e PL image of a 4 × 4 3D matrix code configured with vertical CsPbBr\u003csub\u003e3\u003c/sub\u003e nanowires with two different heights of 30 µm and 15 µm (scale bars: 15 µm). \u003cstrong\u003ed,\u003c/strong\u003e Emission spectra of\u003cstrong\u003e \u003c/strong\u003ethe printed 4 × 4 matrix code pixels with a pump fluence of 10 µJ cm\u003csup\u003e-2\u003c/sup\u003e, exhibiting no lasing action. \u003cstrong\u003ee,\u003c/strong\u003e At a pump fluence of 30 µJ cm\u003csup\u003e-2\u003c/sup\u003e, only 30 µm-height pixels lase. \u003cstrong\u003ef,\u003c/strong\u003e At 50 µJ cm\u003csup\u003e-2\u003c/sup\u003e, all of the pixels lase. \u003cstrong\u003eg,\u003c/strong\u003e Mode spacing map of the corresponding matrix code pixels at a pump fluence of 50 µJ cm\u003csup\u003e-2\u003c/sup\u003e. \u003cstrong\u003eh,\u003c/strong\u003e Mode spacing(Δλ)-based quick-response (QR) code: “1” denotes Δλ \u0026gt; 3 nm. \u003cstrong\u003ei,\u003c/strong\u003e QR code: “1” denotes Δλ \u0026lt; 3 nm.\u003c/p\u003e","description":"","filename":"4.png","url":"https://assets-eu.researchsquare.com/files/rs-5651743/v1/7531bd2bf8c762bc0c32d22d.png"},{"id":71635090,"identity":"df565f53-d001-48ec-8e93-31883ffabeac","added_by":"auto","created_at":"2024-12-17 10:05:21","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":6698727,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-5651743/v1/4bf5c7b9-9a20-49dd-a782-c335eccc1cd3.pdf"}],"financialInterests":"The authors declare no competing interests.","formattedTitle":"\u003cp\u003e\u003cstrong\u003eNanoprinting with Crystal Engineering for Perovskite Lasers\u003c/strong\u003e\u003c/p\u003e","fulltext":[{"header":"Introduction","content":"\u003cp\u003eOver the past decade, inorganic lead halide perovskites, particularly CsPbX\u003csub\u003e3\u003c/sub\u003e (X\u0026thinsp;=\u0026thinsp;Cl, Br, I), have emerged as a promising semiconducting material for next-generation information technology\u003csup\u003e\u003cspan additionalcitationids=\"CR2\" citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e\u003c/sup\u003e. They show great potential for diverse fields of applications including solar cells\u003csup\u003e\u003cspan additionalcitationids=\"CR5\" citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e\u003c/sup\u003e, light-emitting diodes\u003csup\u003e\u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e, \u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e\u003c/sup\u003e, photodetectors\u003csup\u003e\u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e, \u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e\u003c/sup\u003e, and lasers\u003csup\u003e\u003cspan additionalcitationids=\"CR12 CR13\" citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e\u003c/sup\u003e due to their outstanding optoelectronic properties\u003csup\u003e\u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e\u003c/sup\u003e and solution processability\u003csup\u003e\u003cspan additionalcitationids=\"CR17\" citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e\u003c/sup\u003e. Recently, extensive research has focused on excellent coherent light emission properties of perovskites for laser applications\u003csup\u003e\u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e, \u003cspan additionalcitationids=\"CR20\" citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e21\u003c/span\u003e\u003c/sup\u003e. Many types of perovskite lasers in the forms of films, disks, and wires have successfully been devised for optical communication\u003csup\u003e\u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e22\u003c/span\u003e\u003c/sup\u003e, sensing\u003csup\u003e\u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e23\u003c/span\u003e\u003c/sup\u003e, and information storage\u003csup\u003e\u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e, \u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e22\u003c/span\u003e, \u003cspan additionalcitationids=\"CR25 CR26 CR27 CR28\" citationid=\"CR24\" class=\"CitationRef\"\u003e24\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e29\u003c/span\u003e\u003c/sup\u003e. Here, a key element to design and engineer lasing characteristics is tailoring the cavity geometry.\u003c/p\u003e \u003cp\u003eTo date, most of the perovskite research has been conducted in the form of a thin film\u003csup\u003e\u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e, \u003cspan citationid=\"CR30\" class=\"CitationRef\"\u003e30\u003c/span\u003e, \u003cspan citationid=\"CR31\" class=\"CitationRef\"\u003e31\u003c/span\u003e\u003c/sup\u003e. Despite the solution processability, the fabrication of micro- and nanostructured perovskite lasers strongly relies on expensive lithographic techniques such as electron beam lithography\u003csup\u003e\u003cspan citationid=\"CR32\" class=\"CitationRef\"\u003e32\u003c/span\u003e, \u003cspan citationid=\"CR33\" class=\"CitationRef\"\u003e33\u003c/span\u003e\u003c/sup\u003e, photolithography\u003csup\u003e\u003cspan citationid=\"CR34\" class=\"CitationRef\"\u003e34\u003c/span\u003e, \u003cspan citationid=\"CR35\" class=\"CitationRef\"\u003e35\u003c/span\u003e\u003c/sup\u003e, imprinting\u003csup\u003e\u003cspan citationid=\"CR36\" class=\"CitationRef\"\u003e36\u003c/span\u003e, \u003cspan citationid=\"CR37\" class=\"CitationRef\"\u003e37\u003c/span\u003e\u003c/sup\u003e, and so on. Furthermore, multiple lithographic processes may be necessary for more sophisticated structuring\u003csup\u003e\u003cspan additionalcitationids=\"CR39\" citationid=\"CR38\" class=\"CitationRef\"\u003e38\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR40\" class=\"CitationRef\"\u003e40\u003c/span\u003e\u003c/sup\u003e.\u003c/p\u003e \u003cp\u003ePrinting technology, e.g., inkjet printing, provides a simple and flexible route to fabricate large-area perovskite micropatterns with controlled geometries and locations\u003csup\u003e\u003cspan additionalcitationids=\"CR42 CR43 CR44 CR45 CR46\" citationid=\"CR41\" class=\"CitationRef\"\u003e41\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR47\" class=\"CitationRef\"\u003e47\u003c/span\u003e\u003c/sup\u003e. However, the conventional approaches continue to suffer from the technological challenges associated with their poor spatial resolution and in-plane low aspect ratio, limiting the design and manufacture of miniaturized perovskite lasers. The utilization of chemically synthesized perovskite micro- and nanowires as a building block provides a beneficial route for miniaturization, however, their placement and assembly suffer from low-yield, labor-intensive processes. Moreover, most fabrication techniques render the nanowire a horizontal geometry in direct contact with the substrate along the entire length, leading to larger index matching and cavity loss\u003csup\u003e\u003cspan citationid=\"CR48\" class=\"CitationRef\"\u003e48\u003c/span\u003e, \u003cspan citationid=\"CR49\" class=\"CitationRef\"\u003e49\u003c/span\u003e\u003c/sup\u003e.\u003c/p\u003e \u003cp\u003eIn this work, we develop a nanoscale, crystal-engineered 3D printing method for fabricating vertical nanowires for high-performance lasing. We harness electrohydrodynamic (EHD) nanodripping to print CsPbBr\u003csub\u003e3\u003c/sub\u003e precursor nanodroplets directly on the substrate, followed by evaporation-driven crystallization. With the aid of electrostatic autofocusing, the EHD nanodripping produces a freestanding nanowire with tailored diameter, length, and placement. Subsequent vapor-phase solvent annealing significantly improves the crystallinity of the printed freestanding nanowire with large refractive index contrast with the surrounding air, leading to high-performance two-photon pumped lasing with a lasing threshold of 2.98 \u0026micro;J/cm\u003csup\u003e2\u003c/sup\u003e. Benefiting from on-demand control of the nanowire length, we demonstrate the capability of selecting the lasing mode and modulating the mode spacing at will. This on-demand approach successfully demonstrates 3D printing of multi-level anticounterfeiting labels configured with sub-micrometer-sized pixels storing the information in individually programmed length-dependent-lasing threshold and mode spacing. The unique features of this method such as nanoscale resolution, lithography-free approach, and exceptional manufacturing flexibility will find a great advance in the practical realization of new-design photon sources.\u003c/p\u003e"},{"header":"Results","content":"\u003cdiv id=\"Sec3\" class=\"Section2\"\u003e \u003ch2\u003e3D printing process with two-step crystal engineering\u003c/h2\u003e \u003cp\u003eFigure \u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003ea depicts our EHD 3D printing process of vertical perovskite nanowires. A glass nanopipette (diameter: 450 nm, Figure S1) filled with CsBr\u0026thinsp;+\u0026thinsp;PbBr\u003csub\u003e2\u003c/sub\u003e precursor ink dissolved in dimethyl sulfoxide (DMSO) is placed above a glass substrate at a separation of 10 \u0026micro;m. A back electrode is located underneath the substrate. The positions of both the pipette and the substrate are controlled by three-axis stepping motors with sub-micrometer accuracy and millimeter displacement capability. When a high voltage of ~\u0026thinsp;10\u003csup\u003e2\u003c/sup\u003e V is applied to the back electrode, an induced electrostatic stress acting on an ink meniscus exceeds the surface tension, and nano-sized ink droplets are ejected out of the pipette and land on the substrate. With the aid of mild substrate heating at 40\u0026deg;C and solvent evaporation, the concentration of the precursor rapidly reaches supersaturation, promoting the crystallization of CsPbBr\u003csub\u003e3\u003c/sub\u003e inside the deposited droplets, which refers to the first-step crystal engineering. Thanks to the electrostatic autofocusing effect\u003csup\u003e\u003cspan citationid=\"CR50\" class=\"CitationRef\"\u003e50\u003c/span\u003e\u003c/sup\u003e, the crystal grows vertically, forming a freestanding CsPbBr\u003csub\u003e3\u003c/sub\u003e nanowire with polycrystalline nature. Note that acquiring high crystallinity and accompanying smooth surface is crucial for lasing performance. To this end, a subsequent vapor-phase solvent annealing process (the second-step crystal engineering) is introduced to the as-printed nanowires. This annealing process uses methanol vapor with high polarity since it is absorbed on the surface of the as-printed structure to decrease the surface energy, leading to recrystallization (See Experimental Section) without shape deformation. Consequently, a high-quality laser cavity with lower surface roughness and excellent crystallinity can be obtained from the as-printed freestanding structure. Figure\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003eb shows the real-time printing process when a pulsed voltage of 180 V with a frequency of 20 Hz and a duty cycle of 60% was applied to the substrate. The process produced a vertical CsPbBr\u003csub\u003e3\u003c/sub\u003e nanowire with a diameter of 550 nm and a length of 5 \u0026micro;m, within 5 seconds.\u003c/p\u003e \u003cp\u003eThe influences of substrate temperature, ink concentration, and applied voltage on the printing were examined. The thermodynamic driving force for crystallization can be quantified by the change in chemical potential\u003cdiv id=\"Equa\" class=\"Equation\"\u003e\u003cdiv format=\"TEX\" class=\"mathdisplay\" id=\"FileID_Equa\" name=\"EquationSource\"\u003e\n$$\\:\\varDelta\\:\\mu\\:=\\:-RT\\text{ln}\\left(\\frac{c}{{c}_{s}}\\right)=-RT\\text{ln}\\sigma\\:\\:\\:\\:\\left(1\\right)$$\u003c/div\u003e\u003c/div\u003e\u003c/p\u003e \u003cp\u003ewhere \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:c\\)\u003c/span\u003e\u003c/span\u003e is the concentration of the precursor in the droplet, \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:{c}_{s}\\)\u003c/span\u003e\u003c/span\u003e is the solubility, \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:R\\)\u003c/span\u003e\u003c/span\u003e is the universal gas constant, \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:T\\)\u003c/span\u003e\u003c/span\u003e is the absolute temperature, and \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:\\sigma\\:\\)\u003c/span\u003e\u003c/span\u003e is the supersaturation ratio. First, we optimized the temperature for reliable printing. An increase in temperature causes the solvent to evaporate, promoting the supersaturation-driven crystallization. If the temperature is too high, it would accelerate the crystallization inside the nanopipette, leading to clogging. On the other hand, if the temperature is too low, solvent evaporation would be insufficient for driving crystallization, leading to the lateral spreading of the ejected ink droplet and end up with failure in vertical crystal growth. Second, the precursor concentration delivers a similar effect as the temperature does. Comprehensively, the diagram in Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003ec shows the printability of a CsPbBr\u003csub\u003e3\u003c/sub\u003e nanowire at different temperatures and ink concentrations. We found a printing success region (marked in green circles) ranging the substrate temperatures from 30 to 50\u0026deg;C and the ink concentrations from 50 to 150 mM. Our EHD printing approach is general and therefore applicable to other perovskite compositions, as Figure S2 shows printed vertical CsPbI\u003csub\u003e3\u003c/sub\u003e and CsPbCl\u003csub\u003e3\u003c/sub\u003e nanowires. The diagrams of their printability are shown in Figures S3 and S4, respectively. The solvent for each perovskite precursor was selected by the consideration of the solubility and the boiling point. For example, a mixture of CH\u003csub\u003e3\u003c/sub\u003eNO\u0026thinsp;+\u0026thinsp;DMSO was used as a solvent for CsPbCl\u003csub\u003e3\u003c/sub\u003e precursor.\u003c/p\u003e \u003cp\u003eThe dependence of the vertical growth speed of perovskites on the applied voltage was quantitatively investigated. Figure\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003ed plots a vertical growth speed of CsPbBr\u003csub\u003e3\u003c/sub\u003e as a function of an applied voltage. The printing was performed at a pipette-substrate distance of 10 \u0026micro;m, a substrate temperature of 40\u0026deg;C, and relative humidity (RH) of 10%. Three distinguishable regions were clearly observed. At a low voltage region below 150 V, no ink ejection was observed (blue cross marks). At a range of 150 V to 180 V, when the induced electrostatic stress acting on the ink meniscus exceeds the surface tension, a periodic ejection of ink nanodroplets produces a freestanding nanowire (green circles). In this region, the growth speed linearly increases with the voltage amplitude, as plotted by the inset of Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003ed. At a voltage over 180 V, there is a big soar in the growth speed due to the ejection of a large-volume ink droplet with an electrostatically driven increase in the ink flow rate (red cross marks), which leads to lateral spreading. The growth speed\u0026ndash;voltage dependencies of CsPbI\u003csub\u003e3\u003c/sub\u003e and CsPbCl\u003csub\u003e3\u003c/sub\u003e were also investigated, as shown in Figures S5 and S6, respectively. The applied voltage influences not only the vertical growth speed but also the diameter of the printed nanowire. Figure\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003ee plots the dependence of the nanowire diameter on the applied voltage. The diameter increases with the voltage, resulting from the increases in the ink flow rate and subsquent limited lateral spreading. The voltage-diameter dependencies of CsPbI\u003csub\u003e3\u003c/sub\u003e and CsPbCl\u003csub\u003e3\u003c/sub\u003e were also demonstrated in Figure S7, exhibiting a similar trend as that of CsPbBr\u003csub\u003e3\u003c/sub\u003e. The results offer a simple, lithography-free route to control the dimension of an individual freestanding nanowire.\u003c/p\u003e \u003cp\u003eTo verify the reliability of the printing, we printed a 20 \u0026times; 20 array of vertical CsPbBr\u003csub\u003e3\u003c/sub\u003e nanowires with programmed heights (Figs.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003ef and \u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003eg). We also fabricated an \u0026lsquo;HKU\u0026rsquo;-shaped nanopattern consisting of three compositions with different emission wavelengths, H: CsPbI\u003csub\u003e3\u003c/sub\u003e; K: CsPbBr\u003csub\u003e3\u003c/sub\u003e; U: CsPbCl\u003csub\u003e3\u003c/sub\u003e (Figure S8). Furthermore, the universality of our method was demonstrated by the fabrication of CH\u003csub\u003e3\u003c/sub\u003eNH\u003csub\u003e3\u003c/sub\u003ePbX\u003csub\u003e3\u003c/sub\u003e (X\u0026thinsp;=\u0026thinsp;Cl, Br, I) nanowires, as shown in Figure S9. The printed nanowires were thermally annealed under 70℃ before the characterization.\u003c/p\u003e \u003cp\u003eThe as-printed CsPbBr\u003csub\u003e3\u003c/sub\u003e nanowire exhibited a polycrystalline nature, as confirmed by the field emission scanning electron microscope (FE-SEM) image, the selected area electron diffraction (SAED) analysis and the bright-field transmission electron microscope (TEM) image in Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003eh, \u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003ei, and \u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003ej, respectively. We remark the vapor-phase solvent annealing improves the crystallinity and the surface smoothness without any structural collapse. The FE-SEM image of Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003ek shows a smooth surface of the printed nanowire after the solvent annealing. Furthermore, the solvent annealing process made a great advancement in improving the crystallinity, as shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003el. The SAED pattern exhibits a single crystal-like pattern which confirmed that the increased grain size and the corresponding HR-TEM image (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003em\u003cb\u003e)\u003c/b\u003e also verified the highly ordered crystallinities of the CsPbBr\u003csub\u003e3\u003c/sub\u003e crystals which enable them to act as a high-quality laser cavity. The bright-field TEM image in Figure S10 also demonstrates the improvement on surface smoothness.\u003c/p\u003e \u003c/div\u003e\n\u003ch3\u003eLasing of 3D printed perovskite nanowires\u003c/h3\u003e\n\u003cp\u003eThe printed vertical CsPbBr\u003csub\u003e3\u003c/sub\u003e nanowire treated with solvent annealing performs high-performance room-temperature lasing, as it acts as a gain medium and high-quality cavity simultaneously. The resulting nanowire geometry provides the designed cavity length and the reflective end facets. It is worth noting that our EHD printing can produce freestanding vertical CsPbBr\u003csub\u003e3\u003c/sub\u003e nanowires, rendering a vertical geometry that leads to large refractive index mismatch and lower cavity loss. The refractive index contrast between the vertical CsPbBr\u003csub\u003e3\u003c/sub\u003e nanowire (n\u0026thinsp;=\u0026thinsp;2.3) and the environment (air, n\u003csub\u003eair\u003c/sub\u003e = 1.0 for one end, glass, n\u003csub\u003eglass\u003c/sub\u003e = 1.5 for the other end) develops more efficient facet reflection and waveguiding along the nanowire than the conventional in-plane geometry. The lasing was stimulated by a two-photon pumped excitation using an 800 nm femtosecond laser at room temperature. The kinetics of two-photon absorption (2PA) is summarized in Figure S11.\u003c/p\u003e \u003cp\u003eFigure \u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ea shows the photoluminescence (PL) spectra of a vertical CsPbBr\u003csub\u003e3\u003c/sub\u003e nanowire with a length of 50 \u0026micro;m, excited with different pump fluences. At a pump fluence, P\u0026thinsp;=\u0026thinsp;1.58 \u0026micro;J cm\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e, the spontaneous emission with relatively broad spectra width was dominated (blue spectrum). With increasing the pump fluence (P\u0026thinsp;\u0026ge;\u0026thinsp;2.98 \u0026micro;J cm\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e), the emission spectra contain a set of sharp peaks at λ \u0026asymp; 542 nm, exhibiting the stimulated emission. It is clearly shown that the FP-mode lasing of the nanowire was produced at high pump fluences. Figure\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003eb plots the emission intensity (left axis, light input-light output, or \u0026lsquo;L-L\u0026rsquo; curve, red) and the full width at half maximum (FWHM) of the primary peak at λ\u0026thinsp;\u0026asymp;\u0026thinsp;542 nm (right axis, blue) as a function of the pump fluence, showing clear evidence of the lasing action. We observed a transition from spontaneous emission to stimulated emission at a threshold of 3.12 \u0026micro;J cm\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e. At above the threshold, the lasing peak intensity increases linearly with the pump fluence. The FWHM of the peak at λ\u0026thinsp;\u0026asymp;\u0026thinsp;542 nm was drastically narrowed down from 12 nm to 0.2 nm at the threshold pump fluence, confirming the occurrence of lasing. The quality factor of this nanowire laser, defined as Q\u0026thinsp;=\u0026thinsp;λ/FWHM, was measured as \u0026asymp;\u0026thinsp;2700. The inset in Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003eb plots the emission intensity as a function of the detection polarization angle, confirming a linearly polarized lasing emission. The vapor-phase solvent annealing significantly influences the lasing threshold. As the solvent annealing time increased from 0 (thermal annealed) to 3 hours, the lasing threshold decreased from 60.48 \u0026micro;J cm\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e to 3.12 \u0026micro;J cm\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e as plotted in Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ec. Similarly, the pump fluence value at the sharp FWHM drop decreased as the solvent annealing time increased (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ed). The dependence of the lasing threshold on the solvent annealing time is plotted in Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ee. The lasing threshold successfully descended down to 2.98 \u0026micro;J cm\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e as the annealing lasted 20 hours. A plateau region was observed due to the limited interdiffusion length of the solvent vapor which accounts for the saturation of the solvent annealing effects\u003csup\u003e\u003cspan citationid=\"CR51\" class=\"CitationRef\"\u003e51\u003c/span\u003e\u003c/sup\u003e.\u003c/p\u003e \u003cp\u003eThe effect of the vertical configuration on the lasing performance was investigated and summarized in Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ef. The lowest lasing threshold of 6.848 \u0026micro;J cm\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e was obtained from a vertical nanowire with solvent annealing, whereas the highest threshold of 43.636 \u0026micro;J cm\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e was obtained from the as-printed nanowire lying on the substrate. Notably, our freestanding CsPbBr\u003csub\u003e3\u003c/sub\u003e nanowires exhibited a better lasing performance regarding the lasing threshold and Q factor than those lying on the in-plane substrate obtained from other conventional methods \u003cb\u003e(\u003c/b\u003eFig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003eg\u003cb\u003e)\u003c/b\u003e.\u003c/p\u003e\n\u003ch3\u003eBespoke nanowire lasers\u003c/h3\u003e\n\u003cp\u003eOur 3D printing approach provides exceptional flexibility to tailor the nanowire dimension, that is the geometry of the laser cavity. In this study, we demonstrated on-demand length control of the nanowire for individual modulation of lasing characteristics, as depicted in Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ea. The nanowire length is a key parameter to tuning the lasing action in FP mode. Figure\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003eb shows lasing spectra for freestanding nanowires with a diameter of 850 nm and different lengths, \u003cem\u003eL\u003c/em\u003e from 10 \u0026micro;m, 14 \u0026micro;m, 20 \u0026micro;m, 30 \u0026micro;m, 40 \u0026micro;m, to 50 \u0026micro;m, under femtosecond pulsed laser excitation (800 nm, 50 fs, 1 kHz). In the spectra, the number of modes showed a descending trend when decreasing \u003cem\u003eL\u003c/em\u003e and as a result, a single-mode lasing spectrum was acquired at \u003cem\u003eL\u003c/em\u003e\u0026thinsp;=\u0026thinsp;10 \u0026micro;m. All the spectra present a series of peaks with different mode spacing (△λ) values. It is noteworthy that the mode spacing, △λ is found to have a linear relationship with the reciprocal of \u003cem\u003eL\u003c/em\u003e. According to the FP mode laser theory, the equation △λ\u0026thinsp;=\u0026thinsp;λ\u003csup\u003e2\u003c/sup\u003e/2n\u003csub\u003eg\u003c/sub\u003eL (n\u003csub\u003eg\u003c/sub\u003e: group refractive index of the gain material, \u003cem\u003eL\u003c/em\u003e: length of the nanowire, λ: emission wavelength) agrees with the experimental results (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ec). From the linear fitting of △λ \u0026ndash; 1/\u003cem\u003eL\u003c/em\u003e relation with a slope of 68, n\u003csub\u003eg\u003c/sub\u003e of the printed CsPbBr\u003csub\u003e3\u003c/sub\u003e nanowire at λ\u0026thinsp;\u0026asymp;\u0026thinsp;542 nm is determined to be 2.2, which is consistent with the reported value of 2.3\u003csup\u003e52\u003c/sup\u003e. The lasing threshold decreases as \u003cem\u003eL\u003c/em\u003e increases, as plotted in Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ed. This trend may be attributed to the gain volume change as the length, similar to that seen in the previous report\u003csup\u003e\u003cspan citationid=\"CR53\" class=\"CitationRef\"\u003e53\u003c/span\u003e\u003c/sup\u003e.\u003c/p\u003e \u003cp\u003e \u003cb\u003eFreestanding nanowire lasers as cryptographic primitives.\u003c/b\u003e \u003c/p\u003e \u003cp\u003eThe ability of our technique to tailor nanowire lasers leads to high-resolution printing of multilevel anticounterfeiting labels. For a proof-of-concept demonstration, we fabricated a 4 \u0026times; 4 matrix code consisting of vertical CsPbBr\u003csub\u003e3\u003c/sub\u003e nanowires with two different lengths of 30 \u0026micro;m and 15 \u0026micro;m for pixels, as depicted in Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003ea. The nanowires have a diameter of 850 nm with a pitch (wire-to-wire distance) of 15 \u0026micro;m. The first level of security comes from the nanowires\u0026rsquo; small diameter with a vertical configuration, only visible via a high-magnification microscope (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003eb). A second security level is that the fluorescence nature of the perovskite nanowires is only accessible by specific light excitation with an appropriate wavelength, as demonstrated in Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003ec. We point out that the nanowire\u0026rsquo;s length-dependent-lasing can be another level of cryptographic primitive. At a relatively low pump fluence of 10 \u0026micro;J/cm\u003csup\u003e2\u003c/sup\u003e, all 16 pixels in the printed matrix code exhibited broad spontaneous emissions corresponding to the fluorescence of CsPbBr\u003csub\u003e3\u003c/sub\u003e (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003ed). Their indistinguishable emission spectra may protect the nanowire length information from duplication. At a pump fluence of 30 \u0026micro;J/cm\u003csup\u003e2\u003c/sup\u003e, the pixels configured with the 30 \u0026micro;m-length nanowire exhibited lasing action due to their lower lasing threshold value (22.8 \u0026micro;J/cm\u003csup\u003e2\u003c/sup\u003e) than the applied power, whereas the others still exhibited spontaneous emission, as shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003ee. The result demonstrates that the pump fluence can be a cipher key for accessing the length-dependent laser characteristics of the nanowire pixels. When the pump fluence exceeds 50 \u0026micro;J/cm\u003csup\u003e2\u003c/sup\u003e, all 16 pixels exhibited lasing emissions but their different mode spacings (△λ) depended on the nanowire lengths (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003ef). The average △λ values for the 30 \u0026micro;m and 15 \u0026micro;m-length nanowires were 2.18\u0026thinsp;\u0026plusmn;\u0026thinsp;0.15 nm and 4.02\u0026thinsp;\u0026plusmn;\u0026thinsp;0.21 nm, respectively. Figure\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003eg shows the mode spacing mapping of the corresponding matrix code at 50 \u0026micro;J/cm\u003csup\u003e2\u003c/sup\u003e. This length-dependent △λ can be used as a cryptographic primitive and Figs.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003eh and \u003cb\u003ei\u003c/b\u003e show examples of how to decrypt △λ information of individual pixels. Figure\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003eh shows a △λ-based quick-response (QR) code generated by a condition if \u0026ldquo;1\u0026rdquo; denotes \u0026ldquo;△λ\u0026thinsp;\u0026gt;\u0026thinsp;3 nm\u0026rdquo; and \u0026ldquo;0\u0026rdquo; denotes else. The △λ-based QR code can be variable. The reversed QR code is generated by changing the condition to if \u0026ldquo;1\u0026rdquo; denotes \u0026ldquo;△λ\u0026thinsp;\u0026lt;\u0026thinsp;3 nm\u0026rdquo; and \u0026ldquo;0\u0026rdquo; denotes else (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003ei). It is noteworthy that such encoded mode spacing can only be decrypted by high-precision analysis of the lasing spectra, inaccessible via conventional imaging. From this, we show that we can freely encrypt information in the length of the vertical nanowire pixel and read it out by analyzing the lasing mode spacing, which offers another level of security for these anticounterfeiting labels. Last but not least, the data-storage capacity and security level can be easily enhanced by a combination of different nanowire lengths and compositions via our advanced 3D printing technique.\u003c/p\u003e"},{"header":"Discussion","content":"\u003cp\u003eIn this work, we have developed a nanoscale electrohydrodynamic 3D printing method combined with vapor-phase solvent engineering to directly print freestanding perovskite nanowire lasers. This method enables on-demand, precise control over dimension and placement in miniaturized perovskite lasers, by which the two photon-pumped emission characteristics can be tailored at will. Furthermore, subsequent vapor-phase solvent annealing improves the crystallinity of printed nanowires which makes a joint contribution with the vertical geometry to the high-performance lasing. CsPbBr\u003csub\u003e3\u003c/sub\u003e vertical nanowires with different lengths were successfully fabricated, which were found to realize FP mode lasing with programmed mode spacing and threshold power. The proof-of-concept experiments demonstrate multi-level cryptographic anticounterfeiting labels configured with 3D perovskite nanopixels with individually programmed lasing characteristics, which are inaccessible via conventional optical imaging apparatus. These results provide the engineering basis for the function-oriented design of diverse perovskite laser devices without the restriction of traditional lithographic processes and the novel insight into high-resolution information encryption and storage.\u003c/p\u003e"},{"header":"Materials and Methods","content":"\u003cp\u003e\u003cstrong\u003e7.1\u0026nbsp;\u003c/strong\u003e\u003cstrong\u003eMaterials and Synthesis of Functional Inks\u003c/strong\u003e: Cesium iodide (CsI, 99.998%, purchased from Alfa Aesar) and lead (II) iodide (PbI\u003csub\u003e2\u003c/sub\u003e, 99%, purchased from Sigma Aldrich), Cesium bromide (CsBr, 99.999%, purchased from Alfa Aesar) and lead (II) bromide (PbBr\u003csub\u003e2\u003c/sub\u003e, 99%, purchased from TCL), Cesium chloride (CsCl, 99.999%, purchased from Alfa Aesar) and lead (II) chloride (PbCl\u003csub\u003e2\u003c/sub\u003e, 99%, purchased from TCL) were used as solutes. Dimethyl sulfoxide (DMSO) (99.7%, purchased from Acros), and formamide (CH\u003csub\u003e3\u003c/sub\u003eNO, 99.5%, purchased from Acros) were used as solvents. 0.3 M CsPbI\u003csub\u003e3\u003c/sub\u003e precursor solution ink was prepared by dissolving 0.3 mmol CsI and 0.3 mmol PbI\u003csub\u003e2\u003c/sub\u003e into 1 mL DMSO with overnight stirring at 70 °C for a concentration of 0.3 M. 0.075 M CsPbBr\u003csub\u003e3\u003c/sub\u003e precursor solution ink was prepared with dissolving 0.075 mmol CsBr and 0.075 mmol PbBr\u003csub\u003e2\u003c/sub\u003e into 1 mL DMSO with overnight stirring at 70 °C. 0.1M CsPbCl\u003csub\u003e3\u003c/sub\u003e precursor solution ink was prepared by dissolving 0.1 mmol CsCl and 0.1 mmol PbCl\u003csub\u003e2\u003c/sub\u003e into 1 mL CH\u003csub\u003e3\u003c/sub\u003eNO with overnight stirring at 70 °C and then diluted by DMSO with a volume ratio of 2:1. The ink preparation was performed in a glovebox with controlled oxygen concentration and humidity.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003e7.2\u0026nbsp;\u003c/strong\u003e\u003cstrong\u003ePreparation of Nozzles\u003c/strong\u003e: 450 nm-aperture borosilicate nanopipettes (filament embedded, purchased from World Precision Instruments) were fabricated by a programmed heat-pulling process (P-97 Flaming/Brown Micropipette Puller, purchased from Sutter Instrument). Only pipettes with good nozzle quality, that is to say, with no cracks, or chipped edges were used. The pipette diameter was characterized using an FE-SEM (LEO 1530, Zeiss) installed at the Electron Microscope Unit of the University of Hong Kong.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003e7.3\u0026nbsp;\u003c/strong\u003e\u003cstrong\u003ePreparation of Substrates\u003c/strong\u003e: The glass substrate were cleaned by 5-min ultrasonication in successive volumes of acetone, isopropyl alcohol, ethanol, and deionized water.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003e7.4\u0026nbsp;\u003c/strong\u003e\u003cstrong\u003e3D Printing Process\u003c/strong\u003e: The printing machine consists of an ink-filled nanopipette and a glass substrate, which is spatially controlled by using a three-axis (x, y, z) stepping motor stage (XA05A, ZA05A, Kohzu Precision). Their positions and moving speeds are accurately controlled in real-time under custom-made software. The ink was introduced to the backside opening of the pipette and drawn to the very tip by capillary forces without applying any pressure. Given the small nozzle size, minimal caution was necessary when handling them. The pipette-substate distance was assured by a z-axis movement of the motor stage. The printing process was accomplished by applying a voltage to the glass substrate. The applied voltage was generated by a waveform generator and a high-voltage amplifier. During the printing process, the glass substrate was heated up to 40 °C to accelerate the perovskite crystallization and avoid lateral spreading. After printing, the glass substrate with perovskite nanowires was annealed at 70 °C for 10 mins to make it fully crystallized. The printing process was monitored in real-time by using a side-view optical microscope consisting of a 50× long working distance objective (Mitutoyo) and a camera equipped with a complementary metal-oxide-semiconductor sensor (DCC1545M, Thorlabs). The entire printing process was performed inside a custom-made environmental enclosure (filled with nitrogen gas) at controlled relative humidity and temperature.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003e7.5\u0026nbsp;\u003c/strong\u003e\u003cstrong\u003eSample Characterizations\u003c/strong\u003e: Full characterizations of 3D printed structures were performed in various aspects. The exteriors of the printed nanostructures were characterized by FE-SEM (Zeiss Leo 1530). The chemical compositions were quantitatively analyzed by energy-dispersive X-ray spectroscopy under a 20-kV electron beam of the Leo 1530. The characterization of the 3D printed structures’ crystallinity at a single entity level was conducted with a transmission electron microscope (TEM, FEI Tecnai G2 operating at 300 kV). For preparing the TEM samples, the 3D printed structures were directly fabricated onto a TEM grid (Ted Pella, lacey carbon type-A support film, 300 mesh, copper). Before these characterizations, all the fabricated samples were annealed at 70 °C for 10 mins.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003e7.6\u0026nbsp;\u003c/strong\u003e\u003cstrong\u003eVapor-Phase Solvent Engineering Process\u003c/strong\u003e: the as-printed structure on a glass substrate was put in a petri-dish with a radius 9 cm of and a depth of 1.5 cm. And 20 ml of methanol was injected into the petri-dish. The solvent annealing process was happening in the glove box at room temperature.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003e7.7\u0026nbsp;\u003c/strong\u003e\u003cstrong\u003eLaser Measurements\u003c/strong\u003e: For the laser measurements, a schematic of the laser characterization setup is illustrated in Figure S15. Samples with CsPbBr\u003csub\u003e3\u003c/sub\u003e freestanding nanowires with different lengths were fabricated on a glass substrate by the same protocol mentioned above. The samples were located inside a chamber (Linkam DSC 600 temperature controller stage) connected to a rotary pump. A Ti: sapphire femtosecond laser (Coherent Libra) integrated with an optical parametric amplifier (Coherent OPerA Solo), which generates femtosecond pulses (50 fs, 1 kHz) at 800 nm, was used as the excitation source. The microscope (Olympus BX-52) and an objectives lens (20*0.8 NA objectives lens) were used to focus the femtosecond laser beam to a 200 µm diameter spot. The freestanding nanowires on the substrates were excited by the laser spot. The light emitted from the samples was collected by a conventional charge-coupled device (CCD) camera for the recording of the near-field image or attached to a monochromator (Princeton SpectraPro 2750 integrated with a ProEM EMCCD camera with a spectral resolution less than 0.1 nm) for spectrum analysis.\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003e\u003cstrong\u003eA\u003c/strong\u003e\u003cstrong\u003ecknowledgements\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThis work was supported by the General Research Fund (17208218, 17208919, 17204020) from the Research Grants Council of Hong Kong;\u0026nbsp;the National Natural Science Foundation of China/Research Grants Council Joint Research Scheme (N_HKU743/22);\u0026nbsp;Seed Fund for Basic Research (201910159047, 202111159097) from University Research Committee (URC), The University of Hong Kong; PolyU (RGC) nos. G-UALA, BBA5, ZVDJ and YBVJ; and Sichuan Natural Science Foundation (2022YFH0108);\u0026nbsp;the National Research Foundation of Korea (NRF) grant funded by the Korea government (MSIT) (No. RS-2024-00407084). J.R. acknowledges the National Research Foundation (NRF) grant (RS-2024-00356928) funded by the Ministry of Science and ICT (MSIT) of the Korean government.\u003c/p\u003e\n\u003cp\u003eContributions\u003c/p\u003e\n\u003cp\u003eShiqi Hu designed and performed the experiments and analyzed the data. Ting Wang, Siu Fung Yu contributed to the laser optical characterization and analyzed the data. Mojun Chen, Yu Liu, Heekwon Lee, Jihyuk Yang, Xiao Huan, Tianyu Jiang, Cherry Park, Nara Jeon contributed to the optimization of the 3D printing process and gave helpful discussion. Zhiwen Zhou and Shien-Ping Feng contributed to the ink preparation. Shiqi Hu and Ji Tae Kim wrote the original manuscripts, and Ting Wang, Siu Fung Yu, Junsuk Rho, Mingjian Yuan also contributed to revising the manuscripts. Ji Tae Kim and Junsuk Rho supervised the project. All authors contributed to the data analysis and have approved the final version of this manuscript. Shiqi Hu, Ting Wang, Zhiwen Zhou contributed to this work equally.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eData availability\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe data that support the findings of this study are available from the corresponding author upon reasonable request.\u003c/p\u003e\n\u003cp\u003eConflict of interest\u003cbr\u003e\u0026nbsp;The authors declare no competing interests.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\n\u003cli\u003eAdjokatse S, Fang H-H, Loi MA. \u003cem\u003eMaterials Today\u003c/em\u003e \u003cstrong\u003e20\u003c/strong\u003e, 413-424 (2017).\u003c/li\u003e\n\u003cli\u003eZhou N\u003cem\u003e, et al.\u003c/em\u003e Perovskite nanowire\u0026ndash;block copolymer composites with digitally programmable polarization anisotropy. \u003cem\u003eScience Advances\u003c/em\u003e \u003cstrong\u003e5\u003c/strong\u003e, eaav8141(2019).\u003c/li\u003e\n\u003cli\u003ePan D, Fu Y, Chen J, Czech KJ, Wright JC, Jin S. 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Structuring the cavity that determines lasing mode and performance, however, is mostly limited to chemical synthesis or in-plane multi-step lithographic processes, which lead to high shaping rigidity or poor lasing performance. Here, we introduce a direct electrohydrodynamic three-dimensional printing that produces freestanding, high-performance inorganic perovskite sub-micro lasers with tailored dimensions and locations, assisted by crystal engineering. The printed vertical nanowires exhibit excellent crystallinity after vapor-phase solvent engineering. Therefore, they show a high-performance two-photon pumped Fabry\u0026ndash;P\u0026eacute;rot mode vertical lasing with a threshold of 2.98 \u0026micro;J/cm\u003csup\u003e2\u003c/sup\u003e, and our on-demand printing method provides the simplest route to tune the lasing characteristics such as lasing threshold and mode spacing, by adjusting the printed nanowire length. We demonstrated that the length-dependent lasing in the printed arrays can configure multi-level anticounterfeiting labels. We expect this additive manufacturing approach combined with crystal engineering to improve the design flexibility and performance of micro photonic circuitries.\u003c/p\u003e","manuscriptTitle":"Nanoprinting with Crystal Engineering for Perovskite Lasers","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2024-12-17 09:41:12","doi":"10.21203/rs.3.rs-5651743/v1","editorialEvents":[{"type":"communityComments","content":0}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true}}],"origin":"","ownerIdentity":"e2853cf0-9247-4485-bbe3-317391652806","owner":[],"postedDate":"December 17th, 2024","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"posted","subjectAreas":[{"id":41640219,"name":"Mechanical Engineering"}],"tags":[],"updatedAt":"2024-12-17T09:41:12+00:00","versionOfRecord":[],"versionCreatedAt":"2024-12-17 09:41:12","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-5651743","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-5651743","identity":"rs-5651743","version":["v1"]},"buildId":"qtupq5eGEP_6zYnWcrvyt","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}